LOWER levels of free triiodothyronine within the normal thyroid range are associated with diabetic kidney disease in people with Type 2 diabetes, a new study has found.
The results suggest that differences in thyroid hormones may carry clinical information even when patients do not meet the criteria for thyroid dysfunction.
Researchers conducted a cross-sectional study of 2,945 people with Type 2 diabetes and normal thyroid function who were treated at a hospital in China. Of these participants, 851 had diabetic kidney disease and 2,094 did not.
Diabetic kidney disease was identified through increased urinary albumin or reduced estimated glomerular filtration rate. Participants with Type 1 diabetes, diagnosed thyroid disorders, abnormal thyroid tests or use of thyroid medication were excluded.
The researchers assessed free triiodothyronine, known as FT3; free thyroxine, or FT4; and thyroid-stimulating hormone. Models were adjusted for factors including age, sex, HbA1c, duration of diabetes, body mass index, smoking, alcohol consumption, hypertension and hyperlipidaemia.
Participants with diabetic kidney disease had lower average FT3 levels than those without the condition. FT4 and thyroid-stimulating hormone levels did not differ significantly between the groups.
Compared with participants in the lowest FT3 quartile, those in the three higher quartiles had approximately 37–40% lower adjusted odds of diabetic kidney disease.
The relationship was not linear. Researchers identified an approximate FT3 threshold of 3.09 pg/mL. Below this point, every 1 pg/mL increase in FT3 was associated with a 37.8% reduction in the odds of diabetic kidney disease. Above the threshold, no significant additional association was observed.
Thyroid hormones contribute to metabolism, insulin sensitivity, renal blood flow and glomerular filtration. The researchers suggested that lower FT3 could reflect metabolic disruption, inflammation or changes in the conversion of thyroid hormones associated with kidney disease.
However, the results do not show that low FT3 causes renal damage. Because thyroid hormones and kidney status were measured at the same time, kidney disease itself could contribute to lower FT3.
The hospital-based cohort was also predominantly male and had relatively poor glycaemic control, potentially limiting wider applicability.
Longitudinal research is needed to determine whether FT3 can predict the development or progression of diabetic kidney disease. The findings do not establish a benefit from thyroid-hormone treatment in patients with otherwise normal thyroid function.
Lu T et al. Association between thyroid hormone levels with diabetic kidney disease among euthyroid participants with Type 2 diabetes mellitus: a cross-sectional study. Diabetes Metab Syndr Obes. 2026;19:618165.
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